1. Field of the Invention
The present invention relates to a self-centering control rod linkage that is free to move linearly yet automatically returns to center when the actuating force is removed.
2. Description of Related Art
Certain industrial processes require a control rod mechanism that will move freely in a linear direction (i.e., “side-to-side” or “back-and-forth”) yet return to center when the operator removes the actuating force. For example, a typical hydraulic sliding spool valve may be connected to a self-centering linkage. The spool valve may have a center position with ports configured such that movement of the spool in one direction from center opens a certain combination of ports. Likewise, movement of the spool in the opposite direction from center opens a different combination of ports. At rest the spool is intended to remain in a neutral center position.
Such a spool valve may feature a handle attached to the end of a control rod linkage that is attached to an end of the spool. Prior art self-centering control rod linkages (such as that depicted in FIG. 1) typically utilize a control rod that passes through an opening in some type of support bracket. Springs on either side of the bracket are then attached to the control rod by either a fixed or adjustable collar. The collar traps the spring between the face of the collar and the bracket. With a spring and collar on both sides of the center bracket, the spring preload force positions the rod such that the compressed spring forces on either side of the bracket are balanced and the rod is in a neutral position (equilibrium).
A self-centering control rod linkage is also used in some applications involving certain vehicle transmissions. For example, a continuously variable transmission such as that disclosed in U.S. Pat. No. 6,419,608 (titled “Continuously Variable Transmission” and owned by Fallbrook Technologies) uses a self-centering control rod to shift the transmission between its ranges (forward-neutral-reverse). With the control rod in the center position, the transmission is in neutral. If the control rod is moved one direction from center, power is transferred through the transmission such that it propels the vehicle forward. Movement of the control rod in the opposite direction from center places the transmission in reverse. Accordingly, a need exists for improved self-centering control-rods.